For certain diseases which are localized to a particular part of the body, the systemic administration of drugs for the treatment of these diseases may not be preferred because of the inefficiencies associated with the indirect delivery of the drugs to the afflicted area. Instead, it may be preferred that the drug be directly applied to the diseased tissue. However, such localized delivery of drugs to the walls of lumens, such as blood vessels and ducts, can be problematic since lumens are involved in the transport of body fluids, which tend to carry the drug away from the afflicted area. Thus, there is a need for devices and methods for the localized delivery of drugs to afflicted tissue, especially body lumens.
A number of methods for delivering drugs to body lumens or vessels involve the use of catheters having expandable portions, such as a balloon, disposed on the catheter. For instance, U.S. Pat. No. 5,304,121 to Sahatjian, PCT application WO 95/03083 to Sahatjian et al. and U.S. Pat. No. 5,120,322 to Davis et al. describe medical devices in which the exterior surface of the device is coated with a swellable hydrogel polymer. A solution of a drug to be delivered to the afflicted tissue is incorporated into the hydrogel. The drug is held within the matrix of the hydrogel. In the case where the medical device is a balloon catheter, the drug is delivered by inserting the catheter into the body lumen and expanding the coated balloon against the afflicted tissue of the lumen to force the drug from the hydrogel into the tissue.
However, these hydrogel coated devices have certain disadvantages. In particular, since the hydrogels are water-based, only hydrophilic drugs can be effectively incorporated into the hydrogels. Therefore, a number of useful hydrophobic biologically active materials or drugs, such as dexamethasone, cannot be suitably embedded into these hydrogels. Hence, there is a need for a coating for a medical device which can effectively incorporate such hydrophobic drugs in relatively large quantities.
Also, the application of the hydrogel coating to the balloon usually involves multiple steps because most balloon materials are hydrophobic so that a hydrogel usually has poor adhesion to the balloon surface. Another disadvantage with hydrogels is that the hydrogels will tend to be tacky or sticky when they are not fully hydrated. When a hydrogel is not in its fully hydrated state, it can stick to the surface of the packaging material or protection sheath for the coated device and make the insertion or implantation of the device difficult.
Moreover, even when prostheses having a drug containing coating are implanted into the body, it is desirable to apply a dose of the drug to the implantation site in addition to that contained in the coating. Hence, there is a need for a device which can deliver a prosthesis as well as a dose of the drug to the implantation site.